Flying shear

ABSTRACT

A flying shear has a frame; an upper knife holder set in the frame for free movement forward and backward therein, the top surface of the upper knife holder contacting the frame through intermediate members, the upper knife holder having oscillating arms each extending downward along its respective sides, a lower knife holder moving vertically along the guiding portion of the oscillating arms of the upper knife holder and oscillating integrally with the upper knife holder forward and backward, an oscillating device for oscillating the upper knife holder forward and backward; and a driving device for vertically moving the lower knife holder.

United States Pate 1191 1111 3,872,73 Takubo 1 Mar. 25, 1975 1 FLYING SHEAR 248,837 8/1966 Austria 83/317 [75] Inventor: Koreyasu Takubo, Kitakyushu,

Japan Primary Examiner-Frank T. Yost [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan 57 ABSTRACT [22] Fled: 1973 A flying shear has a frame; an upper knife holder set 2 APPL 370 753 in the frame for free movement forward and backward therein, the top surface of the upper knife holder contacting the frame through intermediate members, the

[52] US. Cl. 83/317, 83/824 upper knife holder having Oscillating arms each [51] Int. Cl B2311 25/06 tending downward along i respective sides a tower [58] Field of Search 83/317, 316, 315, 318, knife holder moving vertically along the guiding pop 1 83/824 tion of the oscillating arms of the upper knife holder and oscillating integrally with the upper knife holder [56] References Cited forward and backward, an oscillating device for oscil- UNITED STATES-PATENTS lating the upper knife holder forward and backward; 3,279,291 10/1966 Brombach Ct al. 83/316 x and a dri ing device for vertically moving the lower 3,437,738 H1970 Bearer 83/316 knife holder.

FOREIGN PATENTS OR APPLICATIONS 10 Claims, 9 Drawing Figures 807,007 1/1959 United Kingdom 83/317 PATENTEU 3.872.753

sumeura SPEED SIGNAL TRANSMITTER EL J I SS PULSE SETTER 9| 83 84 TRANS- SUBTRA- 85 DUCER, CTER 9 5 92 87 9O COMPARA- 88 ORDEQING TOR FLYING SHEAR BACKGROUND OF THE INVENTION The present invention relates to a flying shear for shearing such materials as steel strip or bar into pieces of desired length as the materials are running continuously. There is generally knownthe type of flying shear having the mechanism shown in FIG. 1. In this figure, numeral 1 indicates an upper knife holder, which has an upper knife 2 fixedly contained at the bottom end of its body portion. Numeral 3 indicates a supporting arm projecting from the body portion of said upper knife holder 1, with its lower end connected to the central pivot point of a crank shaft 4 for free rotation relative thereto. Numeral 6 indicates a lower knife holder containing a lower knife 7, such lower knife holder 6 being connected to the eccentric 5 of the crank shaft 4 through a connecting rod 8.

When the eccentric 5 of the crank shaft 4 is turned one revolution the lower knife holder 6 is given vertical movement by means of the connecting rod 8, such movement being for shearing materials. It is well known that the movement of the upper knife holder 1 should be synchronized with the running speed of materials. For this purpose, an oscillating device 9 such as a hydraulic actuating cylinder is connected by the supporting arm 3 to the upper knife holder 1 so as to give the so required reciprocal motion to the upper knife holder 1. It is also known that if the running speed of the material and the speed of revolution of the crank are fixed, the distance S over which the upper knife holder 1 is to travel at such rate so as to be synchronized with the running speed of the material, will also be fixed.

Taking the distance between the running surface L of the material and the upper knife 2 as A, and assuming that the upper knife holder 1 oscillates along a circular are, the upper knife 2 moves downward the distance B, while the upper knife holder progresses through the distance S, thus leaving the thickness of the horizontal open space between both knives as A-B. That is to say, A-B determines the maximum thickness of materials to be subjected toshearing with a specific flyingshear. Therefore, in designing such flying shears particularly for shearing materials of great thickness, it is necessary to make either the distance A or the distance between the upper knife 2 and the center of the crank shaft 4 very great, both of which may cause such disadvantages as a requirement for increased power for driving the crank and of a large size of the mechanical system and of the upper holder, having a structure to withstand the shearing reaction force by itself, necessitating increased power for driving the oscillating device, resulting in greater construction and operation cost; moreover, greater weight of the so designed oscillating members, particularly the upper knife holder ll, may cause slower operations of the shears, making it impossible to shear at a high rate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a flying shear to shear materials at a high shearing capacity in terms of the thickness of such materials.

Another object of the present invention is to provide a flying shear with an upper knife holder which is compact due to a decreased shearing load working thereon.

A further object of the present invention is to provide a flying shear of small size and light weight which can be manufactured at low cost and operated at high operation efficiency.

Other and further objects of the present invention will be apparent from the following explanation in detail and some embodiments thereof.

In order to achieve the abovementioned objects, the flying shear of the present invention comprises a frame; an upper knife holder set in said frame from free movement forward and backward therein, the top surface of the upper knife holder contacting the frame through intermediate members, said upper knife holder having oscillating arms each extending downward along its respective sides, a lower knife holder moving vertically along the guiding portion of the oscillating arms of said upper knife holder and oscillating integrally with said upper knife holder forward and backward, an oscillating device for oscillating said upper knife .holder forward and backward; and a driving device for vertically moving said lower knife holder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a conventional type of flying shear FIG. 2 is a partially cutaway front view of a flying shear of the present invention for the illustration of illustrating one embodiment thereof;

FIG. 3 is a cross-sectional view of the flying shear of FIG. 2 along the line llIlII;

FIG. 4 is a detailed, cross-sectional view of part of the upper knife holder of the flying shear of the present invention;

FIG. 5 is a detailed cross-sectional view of the upper knife holder and part of the frame of the present invention for the illustration of another embodiment thereof;

FIG. 6 is a block diagram of a control system for an oscillating device for the upper knife holder and the lower knife holder and driving device for vertically moving the lower knife holder;

FIG. 7 is a cross-sectional view of a flying shear having an oscillating device for the upper knife holder and the lower knife holder illustrating another embodiment of the same;

FIG. is a cross-sectional view of the main part of a driving device for vertically moving the lower knife holder illustrating another embodiment of the same;

FIG. 9 is a partly cut away elevation view of a driving device for vertically moving the lower knife holder illustrating a further embodiment of the same.

DESCRIPTION OF THE PREFERRED EMBODIMENT The flying shear of the present invention will be explained in reference to embodiments illustrated in the attached drawings.

As shown in FIG. 2, a frame 11 is constructed as a strong, gate-shaped structure with a bed 12, columns 13 and 14 and a cross head 15. Up on the inside surface of each of the columns 13 there is provided a guide ledge 16 extending horizontally in the direction of the pass line for materials M. The bottom surface R7 of the cross head 15 is finished into a surface of great smoothness for the sliding thereon of guide rollers 24 provided on the below-mentioned upper knife holder 21. The frame 11 contains an upper knife holder 21 and a lower knife holder 31, constructed in the following manner;

The upper knife 23 is fixed on the body portion 22 of the upper knife holder 21 along the lower side thereof with the cutting edge pointing downward. Up on both sides of the body portion 22 there are provided guide rollers 24 rolling on the guide ledges 16 on the respective sides. Thus the upper knife holder 21 appears to be suspended in the frame 11. Up on the body portion 22, and between the bottom surface 17 of said cross head and the top surface of the body portion 22, there are provided a plurality of pressure receiving rollers 25 rolling pressed on surface 17 by the force produced from below, each lyingalong the same axis as said guide rollers 24.

Down on the sides of the body portion 22 of the upper knife holder 21 there are provided a pair of oscillating arms 26, one for each side, extending downward. As shown in FIG. 4, each of the oscillating arms 26 is provided with a guide groove 27 with an opening facing inwardly and running from nearly the top thereof downward, and each of said arms 26 has a fork end 28 at the bottom, such fork end 28 being engaged with the hereinafter described slide block 52 for free sliding with a clearance G between the fork end and the slide block.

In the same manner as the body portion 22 of the upper knife holder 21, the body portion 32 of a lower knife holder 31 extends laterally and has a lower knife 33 fixed thereon opposed to the upper knife 23. Both side ends of the body portion 32 of the lower knife holder 31 have guide projections 34 thereon, each such projection being engaged in the guide groove 27 of the respective oscillating arms 27 of the upper knife holder 21.

On the front face of the cross head 15 of the frame 11, there is a projecting a bracket 18, as shown in FIG. 3. On this bracket 18 there is a hydraulic actuating cylinder 41 pivoted for free oscillation by means of a pin 43. The tip of the rod 42 of said hydraulic actuating cylinder 41 is connected to the upper part of the front face of the upper knife holder 21 by a pin 44. This cylinder 41 is for oscillating the upper knife holder 21 and also the lower knife holder 31.

The control system for the oscillating device is shown in FIG. 6, a pulse generator 82 for issuing pulse signals 83 in a number proportionate to the distance over which the to-be-sheared material M travels connected to a measuring roll 81 rolling in contact with the material M. Such pulse signals 83 are sent to a subtracter 84, in which substraction is carried out to determine the difference between the number of pulses of the pulse signals 83 and that of pulses of pulse signals 86 sent from a pulse setter 85 in correspondence with the length desired to be sheared off the material M. A pulse signal 87 representing such difference is sent from the subtracter 84 to an ordering signal generator 88. When the pulse signal 87 is reduced to zero, a signal 89 for ordering start of oscillation (the first ordering signal), is sent from the ordering signal generator 88 to the power source for driving said oscillating device; and at the same time, a pulse generating signal 90 is sent to said pulse setter 85.

On the top surface of the bed 12 of the frame 11, there is mounted a pair of bearings 19, which support a crank shaft 51 extending through the columns 13 and 14. At the positions on the crank shaft 51 corresponding to the fork end 28 of the respective oscillating arms 26 of said upper knife holder 21, there are square slide blocks 52 fitted an the crank shaft 51 for free rotation. These slide blocks 52 are also free sliding in the respective fork ends 28, leaving an appropriate clearance G adjacent the oscillating arms 26. At respective positions on the crank shaft 51 somewhat inwardly from respective guide projections 34 of the lower knife holder 31, there is provided an eccentric 53 having a round cross-section, as shown in FIG. 3, eccentric to the crank shaft 51. On this eccentric 53 is freely rotably mounted the lower end of a connecting rod 54. The upper end is connected with the lower knife holder 31 for free rotation by means of a horizontal pin 35 on the lower part of the body portion 32 of the lower knife holder 31. At the end of the crank shaft 51 on the outside of the column 13 of the frame 11 is provided a brake system consisting of an electromagnetic brake 55; such brake is not limited to this kind; any type of mechanical brakes available on the market can be used. At the other end of the crank shaft 51 on the outside of the column 14, is a motor 58 which is the power source, connected to the shaft 51 through a fly wheel 56 and a clutch 57.

Said crank shaft 51, connecting rod 54, magnetic brake 55, motor 58, etc. together to constitute a driving means for vertically moving the lower knife holder 31.

The control system for the driving device for vertically moving the lower knife holder is, as follows: The pulse signal 83 is sent to a transducer 91, through which said signal 83 is converted into a material speed signal 92. A speed signal transmitter 93 is linked with a member for detecting the running speed of the upper knife 12, such as the hydraulic actuating cylinder 41 of the oscillating device and a signal 94 representing the speed of the upper knife 12 is transmitted from the speed signal transmitter 93. The material speed signal 92 and the upper knife speed signal 94 are applied to a comparator 95; and if and when the speeds represented by these two signals coincide, a shearing starting signal (the second ordering signal) 96 is sent to the driving device for vertically moving said lower knife holder 31.

The flying shear of the present invention which is constructed as described above, operates as follows: As a to-be-sheared material M progresses on a roller table 10 in the direction of the arrow in FIG. 3, its length is being measured by the measuring apparatus until the measured length has come up to the prescribed value, when the first signal is issued. Under the order of the first signal, pressure oil is pumped from an oil pressure pump (not shown) into the hydraulic actuating cylinder 41, which oscillates integrally the upper knife holder 21 and the lower knife holder 3 through the rod 42 around the crank shaft 51 acting as the center of such oscillation. The following explains in detail the process of 0s cillation of the upper knife holder 21 and the lower knife holder 31:

As the upper knife holder 21 moves on the guide ledges 16 provided horizontally inside the frame 11, following the run of the guide rollers 24, there takes place every moment a change of the distance between the center of the crank shaft 51 acting as the center of oscillation and the center of the shaft on which the guide rollers 24 are mounted. But such change is compensated for by the sliding contact of the inner surface of the fork end 28 with the outer surface of the slide block 52.

On the other hand, the top surface of the upper knife holder 21 firmly contacts, through the pressure receiving rollers 21, the bottom surface of the cross head 17 of the frame 11.

When the movement of the upper knife holder 21 and of the lower knife holder 31 coincides with the running speed of the material M, the second signal is issued. Under the order of this signal, the electromagnetic brake 55 is released to activate the clutch 57 so as to transmit the driving power of the motor 58 to the crank shaft 51.

One rotation of the crank shaft 51 causes the lower knife holder 21 to move up by means of the eccentric 53 on the crank shaft 51 and the connecting rod 51, for shearing the material. The return of the same to the waiting position takes place, as follows: The crank shaft 51 having turned one revolutions, the clutch 57 is released under the order of the signal, thereby interrupting the driving power. The crank shaft 41 is braked by the electromagnetic brake 55, so as to set the lower knife holder 31 at the waiting position after it has returned thereto.

On the other hand, when the crank shaft 41 has turned one revolution pressure oil is introduced to the rod side of the hydraulic actuating cylinder 11, by turning a change-over value (not shown) of an oil pressure pump (not shown) working as the driving power source of the oscillating device under the order of the signal, thereby pushing back the rod 12 (to the left side in FIG. 3) so as to return the upper knife holder 21 and the lower knife holder 31 to their waiting positions prior to the shearing operation.

As described above, the flying shear of the present invention is so constructed that the shearing and oscillation systems are contained in the frame mounted on the foundation; that the upper knife holder which is connected with the lower knife holder, is suspended by means of guide rollers from the guide ledges which project from the inside surface of the columns .of the frame with the guide roller supporting surface being level; and that variations of the oscillation radius due to the horizontal movement of said upper knife holder are compensated for by the slide blocks fitted in free sliding relationship in the end part of the oscillating arms, thereby solving the problem of the maximum thickness of to-be-sheared materials, which problem lasts with the flying shear of the conventional type due to the reduction of the distance between the upper knife and the lower knife caused by excessive lowering of the upper knife holder at the time of oscillation. Moreover, the flying shear of the present invention is so constructed that the upward shearing reaction force is borne by the frame itself through rollers, making unnecessary a large equipment size; the compact size of the equipment reduces construction cost and raises shearing efficiency in terms of increased operation rate.

For carrying out the present invention, the abovedescribed device is not the only embodiment, but there can be many modifications thereof, so long as they meet the gist of the present invention, as follows;

The pressure receiving rollers 25 provided on the top surface of the upper knife holder 21, can be replaced by whatever can slide on the upper knife holder 21 and transmit the shearing reaction force to the frame, such as a slider 25a fitted on the upper knife holder 21 as shown in FIG. 5.

The guidance given by the guide ledges 16 provided on the frame 11 and the guide rollers 24, is for the purpose of pressing the pressure receiving rollers 25 against the frame 11, so that this may be achieved by using an elastic body such as a spring between the upper knife holder and the lower knife holder or by using a hydraulic actuating cylinder such as an oil pressure cylinder, so that this can push up the end of the oscillating arms 26.

The'slide block 52 may be positioned at an appropriate position on the frame by fixing devices instead of being mounted on the crank shaft 51. The device for oscillating the upper and the lower knife holder is not limited to the hydraulic actuating cylinder 41, but anything, including a crank, will do, so long as it can reciprocate the upper knife holder 21.

FIG. 7 shows another embodiment of the oscillating device. A pair of bearing blocks 45 fixed on the bed 12 of the frame 11, support a crank shaft 46 for oscillation during free rotation. This crank shaft 46 is provided with an eccentric 417 which has a round section and is mounted eccentrically to the axis of the crank shaft 46. On this eccentric 47 there is rotatably mounted a connecting rod 48 which has its tip linked for free rotation with the lower part of the oscillating arm 26 of the upper knife holder 21 by means of a pin 49. Therefore, the rotation of the crank shaft 46 by means of a driving device 51) linked therewith, causes oscillation of the upper knife holder 21 and the lower knife holder 31.

The ascent of the lower knife holder 31 can be attained by using a wedge member or a link', instead of the crank shaft 51.

FIG. 8 shows another embodiment of the driving device for vertically moving the lower knife holder 31. On the bed 12 of the frame 11 is provided a pair of bearing blocks 61 having respectively a cylindrically shaped recess 62 extending in the direction of the long side of the frame 12. Each bearing block 61 has engaged in the recess 62 a sliding portion 66 of semi-cylindrical shape supporting an oscillating block 63 which oscillates forward and backward. The oscillating block 63 has its top surface slanted downwardly to the right in FIG. 6 (in the direction of the progress of the to-be-sheared materials M), and supports the lower knife holder 31 from below through a wedge member 65. One end of the wedge member 65 is connected with the rod 68 of a hydraulic actuating cylinder 67 held by a holding arm 66 extending from the lower knife hollder 31. The reciprocation of the wedge member 65 causes vertical move ment of the lower knife holder 31. Although not shown in FIG. 8, the lower knife holder 31 is connected with the upper knife holder 21 by means of the guide projection 341, as in the case of the embodiment shown in FIG. 2 and FIG. 3, so that these parts oscillate integrally. In this case, the center of curvature of the sliding surface of said oscillating block 63, constitutes the center of oscillation. The change of the oscilllation radius is compensated for by the sliding of the guide projection 34 of the lower knife holder 31 engaged in the guide groove 27 of the upper knife holder 21.

FIG. 9 shows a further embodiment of a driving device for vertically moving the lower knife holder 31. On the top surface of the bed 12 of the frame 11 are provided a pair of bearing blocks 71 respectively supporting an oscillation-center shaft 72. This oscillationcenter shaft 72 has an oscillating block73 rotatably mounted thereon for free rotation, said oscillating 7 block 73 having a lower link 75 pivoted thereon by means of a pin 74. The lower knife holder 31 is pro- I vided, at its lower part and at the position facing said oscillating block 73, with a pair of upper links 75a pivoted on pins 76 for free rotation. Furthermore, there is provided a hydraulic actuating cylinder 77 horizontally positioned right below the lower knife holder 31 in the direction of the long side of the lower knife holder 31. The base of the hydraulic actuating cylinder 77 is connected with a lower-left link 75 and an upper link 75a by means of apin 79; and the tip of the rod 78 of said hydraulic actuating cylinder 77 is rotatably connected with a lower-right link 75 and the upper link 75a by means of a pin 80.

Thus, the reciprocation of the hydraulic actuating cylinder 77 causes vertical movement of the lower knife holder 31. As in the embodiment shown in FIG. 8, the lower knife holder 31 oscillates integrally with the upper knife holder 21, with the center of such oscillation being at the center of said oscillation-center shaft 72.

What is claimed is:

l. A flying shear comprising a frame; an upper knife holder mounted on said frame for free movement for ward and backward therein, intermediate members between the top surface of the upper knife holder and the frame through which the knife holder contacts the frame, said upper knife holder having oscillating arms extending downward along the respective ends thereof and having guiding portions therealong, a lower knife holder vertically movable along the guiding portions of the oscillating arms of said upper knife holder and oscillating back and forth with said upper knife holder, said knife holders having opposed edges having cutting blades thereon, an oscillating means coupled to said upper knife holder for oscillating said upper knife holder forward and backward; and a driving means coupled to said lower knife holder for vertically reciprocating said lower knife holder toward and away from said upper knife holder.

2. A flyingshear as claimed in claim 1, wherein the frame has vertical columns having horizontal guide ledges therealong, the upper knife holder having rollers on the ends thereof rolling said guide ledges.

3. A flying shear as claimed in claim I, wherein said intermediate members are rollers.

4. A flying shear as claimed in claim 1, wherein said intermediate members are sliders.

5. A flying shear as claimed in claim 1, wherein said oscillating means comprises a hydraulic actuating cylinder supported on the frame and having a rod linked with the upper knife holder.

6. A flying shear as claimed in claim 1, wherein said oscillating means comprises a crank shaft adapted to be driven by a driving device and having an eccentric thereon; and a connecting rod having a base connected to the eccentric on the crank shaft for eccentric rotation therewith and having the tip pivotally connected with the upper knife holder.

7. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises an oscillating block supported for free oscillation forward and backward on said frame; a wedge member freely oscillatable forward and backward between the oscillating block and the lower knife holder; and means coupled to said wedge member for oscillating said wedge member forward and backward.

8. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises a pair of oscillation-center shafts supported on the frame; an oscillating block mounted for free rotation on each oscillation-center shaft, respectively; a first pair of links each having one end pivoted on a corresponding oscillating block, a further pair of links each having one end pivoted on the lower part of the lower knife holder and the other end pivoted to the free end of a corresponding one of the first pair of links; and a hydraulic actuating cylinder positioned horizontally and pivotally connected between the pivotal connections of the corresponding links in the pairs of links.

9. A flying shear as claimed in claim 1, wherein the guiding portions of each of said oscillating arms of the upper knife holder is a guide groove, and the lower knife holder has guide projections thereon engaged in said grooves, and each oscillating arm further has a fork end at the bottom end thereof, and said driving means comprises a crank shaft and an eccentric thereon coupled to said lower knife holder, said crank shaft having slide blocks thereon over which said fork ends are slidably engaged.

10. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises a crank shaft having a pair of eccentrics thereon, connecting rods connecting the lower knife holder to said eccentrics on said crank shaft; a brake coupled to said crank shaft to be released when the movement of the upper knife holder and the lower knife holder coincides with the running speed of the to be-sheared material and to be actuated when the crank shaft has turned one revolution; and a clutch coupled to said crank shaft and adapted to be coupled to a power source and to be released when the crank shaft has turned one revolution. 

1. A flying shear comprising a frame; an upper knife holder mounted on said frame for free movement forward and backward therein, intermediate members between the top surface of the upper knife holder and the frame through which the knife holder contacts the frame, said upper knife holder having oscillating arms extending downward along the respective ends thereof and having guiding portions therealong, a lower knife holder vertically movable along the guiding portions of the oscillating arms of said upper knife holder and oscillating back and forth with said upper knife holder, said knife holders having opposed edges having cutting blades thereon, an oscillating means coupled to said upper knife holder for oscillating said upper knife holder forward and backward; and a driving means coupled to said lower knife holder for vertically reciprocating said lower knife holder toward and away from said upper knife holder.
 2. A flying shear as claimed in claim 1, wherein the frame has vertical columns having horizontal guide ledges therealong, the upper knife holder having rollers on the ends thereof rolling said guide ledges.
 3. A flying shear as claimed in claim 1, wherein said intermediate members are rollers.
 4. A flying shear as claimed in claim 1, wherein said intermediate members are sliders.
 5. A flying shear as claimed in claim 1, wherein said oscillating means comprises a hydraulic actuating cylinder supported on the frame and having a rod linked with The upper knife holder.
 6. A flying shear as claimed in claim 1, wherein said oscillating means comprises a crank shaft adapted to be driven by a driving device and having an eccentric thereon; and a connecting rod having a base connected to the eccentric on the crank shaft for eccentric rotation therewith and having the tip pivotally connected with the upper knife holder.
 7. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises an oscillating block supported for free oscillation forward and backward on said frame; a wedge member freely oscillatable forward and backward between the oscillating block and the lower knife holder; and means coupled to said wedge member for oscillating said wedge member forward and backward.
 8. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises a pair of oscillation-center shafts supported on the frame; an oscillating block mounted for free rotation on each oscillation-center shaft, respectively; a first pair of links each having one end pivoted on a corresponding oscillating block, a further pair of links each having one end pivoted on the lower part of the lower knife holder and the other end pivoted to the free end of a corresponding one of the first pair of links; and a hydraulic actuating cylinder positioned horizontally and pivotally connected between the pivotal connections of the corresponding links in the pairs of links.
 9. A flying shear as claimed in claim 1, wherein the guiding portions of each of said oscillating arms of the upper knife holder is a guide groove, and the lower knife holder has guide projections thereon engaged in said grooves, and each oscillating arm further has a fork end at the bottom end thereof, and said driving means comprises a crank shaft and an eccentric thereon coupled to said lower knife holder, said crank shaft having slide blocks thereon over which said fork ends are slidably engaged.
 10. A flying shear as claimed in claim 1, wherein said driving means for vertically moving the lower knife holder comprises a crank shaft having a pair of eccentrics thereon, connecting rods connecting the lower knife holder to said eccentrics on said crank shaft; a brake coupled to said crank shaft to be released when the movement of the upper knife holder and the lower knife holder coincides with the running speed of the to-be-sheared material and to be actuated when the crank shaft has turned one revolution; and a clutch coupled to said crank shaft and adapted to be coupled to a power source and to be released when the crank shaft has turned one revolution. 